As a measurement device for measuring activity of an ion in a liquid sample by potentiometry, those utilizing dry-type electrodes are widely used.
Such ion activity-measuring devices have at least one pair of electrodes, one of the electrodes being to contact with a liquid sample, and the other being to contact with a reference liquid. The electrode to be contact with the liquid sample is usually imparted with an ion-selective property. When a liquid sample and a reference liquid are brought into contact with the electrodes, the potential difference generated between the electrodes depending on the difference of ion activity is measured, and this potential difference is converted into a concentration.
In order to generate such a potential difference, it is necessary to provide electric conduction between the liquid sample and the reference liquid, and this is realized by providing a bridge between a liquid reservoir for the liquid sample and a liquid reservoir for the reference liquid.
Examples of such a bridge include the slit bridge formed by a Groove such as one disclosed in Japanese Patent Publication (Kokoku) No. 58-4981, in the three-layer tri-laminate bridge made of a porous layer inserted between hydrophobic coating film layers such as one disclosed in Japanese Patent Publication No. 59-4659, the shield type bridge which is a porous bridge composed of regions partitioned by shields that block diffusion of liquid such as one disclosed in Japanese Patent Application Laid-Open (Kokai) No. 58-201056, the thread bridge made of twisted yam such as one disclosed in Japanese Patent Application Laid-Open No. 58-211648 and so forth.